Die head coating, coating device, and method of manufacturing die head for coating

ABSTRACT

During displacement relative to a substrate  1,  a coating die head emits coating liquid out of a slot  12   a  to a surface of the substrate. The coating die head includes a lip  12   b  having a lip surface  12   b  and a side having a side surface  12   c.  A contact angle of the surface  12   c  with respect to the coating liquid is greater than a contact angle of the surface  12   b  with respect to the coating liquid. This configuration enhances stabilization of bead of the coating liquid during application process of the coating liquid, preventing stripes and steps from appearing in the coating layer. This coating die head makes it possible to carry out high precision coating required for fabrication of color filters for liquid crystal displays.

FIELD OF THE INVENTION

The present invention relates to a coating die head, a coatingapparatus, and a method for fabricating a coating die head.

BACKGROUND ART

Commonly, the fabrication of color filters for liquid crystal displaysinvolves the coating of resist liquid onto a substrate, which includes asheet of glass, in order to provide triple-layers of red (R), green (G)and blue (B) or to provide a protective surface layer or geometricshapes. For high precision coating required for the fabrication, spincoating has been used. In spin coating, an excessive amount of resistmaterial, which is costly, is applied onto the surface of a substrate,and the substrate is rotated at a high speed. The spin coating poses theproblem that the radial velocity of the rotating substrate causes asubstantial portion of the resist material to be scattered away from thesubstrate surface, thereby wasting a large amount of the applied resistmaterial and causing high production costs.

This problem of spin coating makes it desirable to improve coatingprocesses by using a coating die head such that the spin coating is nolonger needed.

However, the known coating processes of this kind fail to accomplishdesired thickness uniformity of a coating layer because they allowoccurrence of stripes extending in a direction of the movement of asubstrate and steps lying laterally with respect to the direction of themovement of the substrate.

SUMMARY OF THE INVENTION

In view of the problems with the prior art, the present invention hasbeen devised. An object of the present invention is to provide a coatingdie head, a coating apparatus, and a method for fabricating the coatingdie head, which provide high precision coating required for fabricationof color filters for liquid crystal displays.

Extensive effort made by the inventors to stabilize beads of liquidduring a die head coating process has enabled them to accomplish thepresent invention. Specifically, the inventors found that in making acontact angle of a side surface of a terminal segment of a die head withrespect to the coating liquid greater than a contact angle of a lipsurface of a lip on the terminal segment with respect to the coatingliquid, a point can be maintained at which the uppermost portion of abead of liquid falls off the coating die head always at an area wherethe lip surface and the side surface define therebetween a border line.

According to one exemplary implementation of the present invention,there is provided a coating die head with a slot for emitting coatingliquid to be applied to a substrate, comprising: a lip located on aterminal segment of the coating die head and having a lip surfaceextending from the slot; and a side located on the terminal segment andhaving a side surface inclined to the lip surface, wherein the sidesurface and the lip surface are configured such that a contact angle ofthe side surface with respect to the coating liquid is greater than acontact angle of the lip surface with respect to the coating liquid.

According to another exemplary implementation of the present invention,the coating die head is provided, wherein the side surface and the lipsurface are configured such that the contact angle of the side surfacewith respect to the coating liquid is greater than the contact angle ofthe lip surface with respect to the coating liquid by a difference, inangle, that is greater than or equal to 5 degrees.

According to another exemplary implementation of the present invention,the coating die head is provided, wherein surface material of the sidesurface is different from that of the lip surface.

According to another exemplary implementation of the present invention,the coating die head is provided, wherein surface roughness of the sidesurface is different from that of the lip surface.

According to another exemplary implementation of the present invention,the coating die head is provided, a border line is provided between thelip surface and the side surface and the border line has straightnessand parallelness, with respect to the slot, which are less than or equalto 5 μm/m; wherein, around the border line, a contact angle border lineis provided between the adjacent regions that differ from each other incontact angle with respect to the coating liquid; and wherein adeviation between the contact angle border line and the border line isless than or equal to 5 μm.

According to another implementation of the present invention, there isprovided a coating apparatus comprising: a coating die head with a slotfor emitting coating liquid to be applied to a substrate, the coatingdie head including a lip located on a terminal segment of the coatingdie head and having a lip surface extending from the slot; and a sidelocated on the terminal segment and having a side surface inclined tothe lip surface, wherein the side surface and the lip surface areconfigured such that a contact angle of the side surface with respect tothe coating liquid is greater than a contact angle of the lip surfacewith respect to the coating liquid; and means for carrying out relativedisplacement between the substrate and the coating die head with theterminal segment held in close proximity to the substrate forapplication of the emitted coating liquid to the substrate.

The implementations of the present invention can stabilize bead duringcoating process, preventing occurrence of stripes and steps, which wereapt to be formed in a coating layer applied using a coating die head.Accordingly, if it is used during a resist coating process offabrication of color filters for liquid crystal displays, each of theimplementations of the present invention can carry out high precisioncoating required for the fabrication, making it possible to carry outthe coating process without spin coating, resulting in a cost reduction.

According to another implementation of the present invention, there isprovided a coating die head with a slot for emitting coating liquid tobe applied to a substrate, comprising: a lip located on a terminalsegment of the coating die head and having a lip surface extending fromthe slot; and a side located on the terminal segment and having a sidesurface inclined thereto, wherein surface roughness of the lip surfaceexpressed in terms of the maximum height, Rmax, measured in accordancewith Japanese Industrial Standard JIS B 0601 is less than or equal to0.3 μm.

According to another implementation of the present invention, thecoating die head is provided, wherein the lip surface is of mirrorfinish resulting from super fine grinding.

According to another implementation of the present invention, thecoating die head is provided, wherein the lip surface is of mirrorfinish resulting from electrolytic in-process dressing (ELID) grinding.

According to some of the implementations of the present invention, thelip surface has surface roughness smooth enough to sufficiently suppresslocal changes in contact angle, allowing smooth movement of coatingliquid in such directions as to increase dimension of bead laterallywith respect to a direction of displacement of a substrate relative tothe coating die head during application of the coating liquid to thesubstrate, thus shortening time required for bead build-up. Accordingly,if it is used during a resist coating process of fabrication of colorfilters for liquid crystal displays, the coating die head can carry outhigh precision coating required for the fabrication by shortening asbest as possible a fault range where desired thickness uniformity failsto be accomplished.

According to another implementation of the present invention, thecoating die head is provided, wherein the side surface and the lipsurface are configured such that a contact angle of the side surfacewith respect to the coating liquid is greater than a contact angle ofthe lip surface with respect to the coating liquid.

This configuration can hold a point, at which the uppermost portion ofliquid of bead falls off the coating die head, always at an area wherethe lip surface and the side surface define therebetween a border line.Accordingly, if it is used during a resist coating process offabrication of color filters for liquid crystal displays, the coatingdie head incorporating the above-mentioned configuration can carry outhigh precision coating required for the fabrication by suppressingthickness variation in a coating layer.

According to another implementation of the present invention, thecoating die head is provided, wherein the side surface is made ofelectroless plating of a mixture containing nickel (Ni) and 1 to 10 wt %of fluororesin.

According to another implementation of the present invention, thecoating die head is provided, wherein surface roughness of the sidesurface is different from that of the lip surface.

This implementation of the present invention can hold a point, at whichthe uppermost portion of liquid of bead falls off the coating die head,always at an area where the lip surface and the side surface definetherebetween a border line. Accordingly, if it is used during a resistcoating process of fabrication of color filters for liquid crystaldisplays, the coating die head incorporating this configuration cancarry out high precision coating required for the fabrication bysuppressing thickness variation in a coating layer.

According to another implementation of the present invention, thecoating die head is provided, wherein a border line is provided betweenthe lip surface and the side surface, and the border line hasstraightness and parallelness, with respect to the slot, which are lessthan or equal to 2 μm/m.

If it is used during a resist coating process of fabrication of colorfilters for liquid crystal displays, this implementation of a coatingdie head according to the present invention can carry out high precisioncoating required for the fabrication by shortening as best as possible afault range where desired thickness uniformity fails to be accomplishedduring initial stage of application of the coating liquid to asubstrate.

According to another implementation of the present invention, thecoating die head is provided, wherein, around a border line between thelip surface and the side surface, a contact angle border line isprovided between the adjacent regions that differ from each other incontact angle with respect to the coating liquid; and wherein adeviation between the contact angle border line and the border line isless than or equal to 2 μm.

If it is used during a resist coating process of fabrication of colorfilters for liquid crystal displays, this implementation of a coatingdie head according to the present invention can carry out high precisioncoating required for the fabrication by suppressing thickness variationin a coating layer.

According to another implementation of the present invention, there isprovided a coating apparatus, comprising: a coating die head with a slotfor emitting coating liquid to be applied to a substrate, the coatingdie head including a lip located on a terminal segment of the coatingdie head and having a lip surface extending from the slot; and a sidelocated on the terminal segment and having a side surface inclined tothe lip surface, wherein surface roughness of the lip surface expressedin terms of the maximum height, Rmax, measured in accordance withJapanese Industrial Standard JIS B 0601 is less than or equal to 0.3 μm;and means for carrying out relative displacement between the substrateand the coating die head with the terminal segment held in closeproximity to the substrate for application of the emitted coating liquidto the substrate.

If it is used during a resist coating process of fabrication of colorfilters for liquid crystal displays, this implementation of a coatingapparatus according to the present invention can carry out highprecision coating required for the fabrication by shortening as best aspossible a fault range where desired thickness uniformity fails to beaccomplished during initial stage of application of the coating liquidto a substrate and by suppressing thickness variation in a coatinglayer.

According to another implementation of the present invention, there isprovided a method for fabricating a coating die head with a slot foremitting coating liquid to be applied to a substrate, including a liplocated on a terminal segment of the coating die head and having a lipsurface extending from the slot; and a side located on the terminalsegment and having a side surface inclined to the lip surface, whereinsurface roughness of the lip surface expressed in terms of the maximumheight, Rmax, measured in accordance with Japanese Industrial StandardJIS B 0601 is less than or equal to 0.3 μm, the method comprising thestep of treating the lip surface to application of to mirror finish.

According to this implementation of a method according to the presentinvention, the lip surface has surface roughness smooth enough tosufficiently suppress local changes in contact angle, allowing smoothmovement of coating liquid in such directions as to increase dimensionof bead laterally with respect to a direction of displacement of asubstrate relative to the coating die head during application of thecoating liquid to a substrate, thus shortening time required for beadbuild-up. Accordingly, if it is used during a resist coating process offabrication of color filters for liquid crystal displays, theimplementation of a method according to the present invention can carryout high precision coating required for the fabrication by shortening asbest as possible a fault range where desired thickness uniformity failsto be accomplished.

The coating die head and the coating apparatus according to theimplementations of the present invention may find other applicationsthan a resist coating of the fabrication of color filters for crystaldisplays.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective schematic view of one implementation of acoating die head according to the present invention together with anenlarged view of a portion of this perspective view.

FIG. 2 is a perspective schematic view given by enlarging a terminalsegment of the coating die head.

FIGS. 3( a) and 3(b) are perspective schematic views illustratingprocesses of fabricating the coating die head shown in FIG. 1.

FIG. 4 is a cross sectional schematic view of the coating die head shownin FIG. 1 during application of coating liquid to the surface of asubstrate.

FIG. 5 is a perspective schematic view of a terminal segment of anotherimplementation of a coating die head according to the present invention.

FIG. 6 is a perspective schematic view of a terminal segment of anotherimplementation of a coating die head according to the present invention.

FIG. 7 is a perspective schematic view of one comparative example of acoating die head.

FIG. 8 is a cross sectional schematic view of the comparative example ofthe coating die head during application of coating liquid to the surfaceof a substrate.

FIG. 9 is a cross sectional schematic view of another comparativeexample of a coating die head during application of coating liquid tothe surface of a substrate.

FIG. 10 is a perspective schematic view of another implementation of acoating die head according to the present invention together with anenlarged view of a portion of this perspective view.

FIG. 11 is a perspective schematic view given by enlarging a terminalsegment of the coating die head shown in FIG. 10.

FIGS. 12( a) and 12(b) are perspective schematic views illustratingprocesses of fabricating the coating die head shown in FIG. 10.

FIG. 13 is a cross sectional schematic view of the coating die headshown in FIG. 10 during application of coating liquid to the surface ofa substrate.

FIGS. 14( a), 14(b) and 14(c) are a perspective schematic view of acoating die head emitting coating liquid, an enlarged view of a lip thathas been surface finished using free slurry, and an enlarged of a lipthat has been surface finished using ELID (ELectrolytic In-processDressing) grinding process, respectively.

FIGS. 15( a) and 15(b) are a perspective schematic view of initial beadformed during application of coating liquid using a coating die headincorporating the lip that has been surface finished using free slurry,and a perspective schematic view of initial bead formed duringapplication of coating liquid using a coating die head incorporating thelip that has been surface finished using ELID grinding process,respectively.

FIG. 16 is a perspective schematic view of a terminal segment of anotherimplementation of a coating die head according to the present invention.

FIG. 17 is a perspective schematic view of a terminal segment of anotherimplementation of a coating die head according to the present invention.

FIG. 18 is a perspective schematic view of another comparative exampleof a coating die head during application of coating liquid to thesurface of a substrate.

FIG. 19 is a cross sectional schematic view of another comparativeexample of a coating die head during application of coating liquid tothe surface of a substrate.

FIG. 20 is a cross sectional schematic view of another comparativeexample of a coating die head during application of coating liquid tothe surface of a substrate.

BEST MODE FOR CARRYING OUT THE INVENTION ONE EMBODIMENT ACCORDING TO THEINVENTION

In one embodiment of a coating die head according to the presentinvention, a contact angle of a surface (namely, a side surface) of aside located on a terminal segment of the die head with respect to acoating liquid is greater than a contact angle of a surface (namely, alip surface) of a lip located on the terminal segment with respect tothe coating liquid.

This configuration enhances stabilization of a bead of liquid that isformed between the lip surface and a substrate during application ofcoating liquid to the substrate, allowing the coating die head to carryout high precision coating process at high speed. Preferably, thecontact angle of the side surface with respect to the coating liquid isgreater than the contact angle of the lip surface with respect to thecoating liquid by an angle that is greater than or equal to 5 degrees.If this difference in contact angle is too small, the coating die headfails to satisfactorily stabilize the bead. The greater the differencein contact angle, the more the effectiveness on the stabilization. Thestabilization of the bead creates a condition under which the coatingdie head can carry out more severe application processes for example,increasing the processing speed. Thus, it is preferrable to increase thedifference in contact angle. Concretely, the difference in contact angleis preferably greater than or equal to 10 degrees. More preferably, thedifference in contact angle is greater than or equal to 20 degrees.

There are various examples of accomplishing the above-mentionedconfiguration in which the contact angle of the side surface withrespect to the coating liquid is greater than the contact angle of thelip surface with respect to the coating liquid. One example is makingthe side surface and/or the lip surface of plating or coating. Anotherexample is making the side surface of material different from materialof the lip surface by, for example, fabricating the lip and side asseparate parts of different materials. Finishing the side surface to asurface roughness different from the surface roughness of the lipsurface is still another example. Further, this configuration may beaccomplished by any one of the combinations of the above-mentionedexamples.

As the contact angle of the side surface with respect to the coatingliquid is greater than the contact angle of the lip surface with respectto the coating liquid, this implementation of a coating die head of thepresent invention can maintain a point at which the uppermost portion ofa bead of liquid falls off the die head always at an area where the lipsurface and the side surface define a border line. The border line hasstraightness and parallelness with respect to the slot, which areimportant for suppressing thickness variation in a coating layer. Thus,when high precision coating process required for fabricating of colorfilters is needed, it is preferred that the deviations in thestraightness and parallelness are as small as possible. Concretely, thedeviations are less than or equal to 5 μm/m. Further, the microscopicarea of a region about the border line shows that the side surfaceand/or the lip surface do not necessarily have the same contact angleover the whole area extending to the border line.

Even if a mask is used to cover the lip surface to expose, for example,the side of the terminal segment only during surface treatment to form,as the side surface, a coating layer that has a large contact angle withrespect to the coating liquid, the edge of the coating layer does notalways lie exactly on the border line, but it may extend beyond theborder line or fail to reach it.

When a contact angle border line is provided or defined between theadjacent two regions that differ from each other in contact angle withrespect to the coating liquid to such an extent as to demonstratedifferent identities in contact angle, it is least likely that thecontact angle border line always lies exactly on the border line betweenthe side surface and the lip surface. If a considerable deviation exitsbetween the contact angle border line and the border line, the coatingvariation is likely to occur. To meet demand for high precision coatingrequired for fabrication of color filters, the deviation is preferablyless than or equal to 5 μm/m.

The implementation of a coating apparatus according to the presentinvention comprises means for carrying out relative displacement betweenthe substrate and the coating die head with the terminal segment held inclose proximity to the substrate for application of the emitted coatingliquid to the substrate. Employing this construction makes it possibleto carry out high precision coating on the substrate.

As they can carry out high precision coating, the embodiments of coatingdie head and coating apparatus according to the present invention cancarry out coating of a resist liquid onto a substrate, which includes asheet of glass, in order to provide triple-layers of red (R), green (G)and blue (B) or to provide a protective surface layer or geometricshapes during fabrication of color filters for liquid crystal displays,making it possible to carry out high precision coating required for thefabrication without using spin coating. The coating die head and thecoating apparatus according to the embodiments of the present inventionmay have other applications than a resist coating for the fabrication ofcolor filters for crystal displays.

Referring to the drawings, preferred implementations of the presentinvention are described below. FIG. 1 is a perspective schematic view ofone embodiment of a coating die head 12 according to the presentinvention together with an enlarged view of a portion of thisperspective view. FIG. 2 is a perspective schematic view given byenlarging a terminal segment of the coating die head 12.

Similarly to the conventional one, the coating die head 12 has a slot 12a for emitting coating liquid to be applied, a lip 12 b located on aterminal segment 12 c, 12 b of the coating die head 12 and having a lipsurface 12 b 12 b extending outwardly from the slot 12 a in a directiongenerally normal to the slot 12 a, and a side 12 c located on theterminal segment 12 b, 12 c having a side surface 12 c extendingoutwardly from the surface of the lip 12 b and inclined thereto. Thewhole body of this coating die head 12 is made of stainless steel. Inthis embodiment, the lip surface of the lip and the side surface of theside can be represented by reference numerals 12 b, 12 c respectively.

The lip surface 12 b extends in the normal direction over a width d,which width d normally ranges from 0.1 to 1.0 mm. The lip surface 12 bis a bare surface resulting from exposing a surface of the body of thecoating die head 12 grounded to roughness falling in a range from 0.1 to0.4 μm/m in Rmax. The side surface 12 c consists of a surface layer 13made of material having poor wettability with respect to the coatingliquid, which surface layer has been deposited, by coating or plating,on the bare surface (base surface) of the body of the coating die head12. The surface layer 13 of the side surface 12 c has poor wettabilitywith respect to the coating liquid (and thus a large contact angle withrespect to the coating liquid).

Examples of surface treatment to provide the surface layer 13 areelectroless plating of nickel (Ni), electroless plating of a mixturecontaining nickel (Ni) and fluororesin, and coating of fluororesin.Selection of material for the surface layer 13 can be made such that acontact angle of the side surface 12 c with respect to the coatingliquid is greater than a contact angle of the lip surface 12 b withrespect to the coating liquid. The selection can be made such that, forexample, an angle, by which the contact angle of the side surface withrespect to the coating liquid is greater than the contact angle of thelip surface with the coating liquid, is greater than or equal to 5degrees. Preferably, this angle is greater than or equal to 10 degrees.More preferably, this angle is greater than or equal to 20 degrees.

If the coating liquid is in the form of liquefied resist generally usedfor the fabrication of color filters for liquid crystal displays, acontact angle of the lip surface 12 b with respect to the coating liquidfalls in a range from 7 degrees to 10 degrees. If, under this condition,the surface layer 13 is formed by electroless plating of nickel (Ni), acontact angle of the side surface 12 c with respect to the coatingliquid amounts to 20 degrees, and thus the difference in angle amountsto 10 degrees at least. If the surface layer 13 is formed of fluororesincoating, the contact angle of the side surface 12 c with respect to thecoating liquid amounts to 50 degrees, and thus the difference in angleamounts to 40 degrees at least. The coating of fluororesin is superiorto the electroless plating of nickel (Ni) in providing an increasedcontact angle although the former is inferior to the latter indurability. Incorporating fluororesin into electroless nickel platingresults in providing a contact angle greater than a contact angleprovided by the electroless plating of nickel and also in providingenhanced durability as compared to the coating of fluororesin. Thus, theappropriate proportion of the mixture of nickel and fluororesin can beselected to meet a desired property to be applied the side surface 12 c.The surface layer 13 can extend to cover at least a region, which mightbe covered by the spread of coating liquid during application of thecoating liquid to the substrate.

As shown in FIG. 2, the surface layer 13 extends over the side surface12 c entirely to define an edge exactly lying on a border line betweenthe lip surface 12 b and the side surface 12 c. The border line 14provided between the lip surface 12 b and the side surface 12 c isstraight, and it has straightness and parallelness, with respect to theslot 12 a, which are less than or equal to 5 μm/m.

In order to form the surface layer 13 to the edge exactly lying on theborder line 14 having the straightness and parallelness less than orequal to 5 μm/m, the material of the surface layer 13 is deposited, byplating or coating, over the entire surface area of not only the sidesurface 12 c, but also the lip surface 12 b as shown in FIG. 3( a).Subsequently a portion of the material is removed, by polishing, toexpose the surface of the lip 12 b and the edge of the surface layer 13as shown in FIG. 3( b).

For application of the coating liquid using the coating die head 12, theterminal segment 12 b, 12 c of the coating die head 12 is held in closeproximity to the surface of a substrate 1 placed on a chuck (notillustrated) as shown in FIG. 4, and the substrate is moved relative tothe coating die head 12. The coating die head 12 emits the coatingliquid to be applied to the substrate 1, forming bead 3 between the lipsurface 12 b and the substrate 1, applying a portion separated from thebead 3 to the substrate 1.

As descried before, the contact angle of side surface 12 c with respectto the coating liquid is greater than that of the lip surface 12 b,which the bead 3 contacts with, causing the side surface 12 c todemonstrate poor wettability as compared to the lip surface. Thisconfiguration can maintain a point A or B, at which the uppermostportion of the bead 3 of liquid falls off the coating die head 12,always at an area where the lip surface 12 b with good wettability andthe side surface 12 c with poor wettability define therebetween theborder line 14. During application of the coating liquid to thesubstrate 1, the bead 3 is kept stabilized, applying the coating liquidto the substrate 1 without allowing appearances of any stripes and stepsconventionally experienced. Thus, a coating layer 4 can be formed sothat the coating layer 4 has accomplished thickness uniformity bysuppressing thickness variation to a sufficiently low level (forexample, thickness variation within ±3% of the layer thickness).Accordingly, if it is used during a resist coating process offabrication of color filters for liquid crystal displays, this coatingdie head 12 can carry out high precision coating (for example, thicknessvariation within ±3% of the layer thickness) required for thefabrication. The spin coating generally employed is no longer needed.

In the above-described implementation, the bare surface of the bodymakes the lip surface 12 b and the surface layer 13 that has poorwettability makes the side surface 12 c, providing the side surface witha contact angle greater than that of the lip surface. The presentinvention is not limited to this implementation and may be accomplishedby covering the lip surface 12 b with a surface layer that haswettability superior to that of the bare surface of the body, and makingthe side surface 12 c by the bare surface of the body. Another approachto accomplish the present invention involves covering the lip surface 12b with one surface layer that has good wettability and covering the sidesurface 12 c with another surface layer that has poor wettability.

The surface treatment like plating or coating is just an example ofaltering contact angles of the lip surface 12 b and the side surface 12c. The contact angles may be altered in any other appropriate manner.Referring to FIG. 5, a coating die head 12A includes separate members ofdifferent materials as portions 16 and 17, respectively, which make alip surface 12 b and a side surface 12 c. Referring to FIG. 6, althoughit is made of the same material, a coating die head 12B is produced by asurface treatment to give a lip surface 12 b more roughness to providegood wettability (reduced contact angle), and by another surfacetreatment to give a side surface 12 c less roughness to provide poorwettability (increased contact angle). Using these measures, the contactangle of the side surface can be made greater than the contact angle ofthe lip surface. The contact angles of the lip surface and the sidesurface may be altered by appropriately combining a selection inmaterial with a selection in surface treatment to provide roughness.

It is likely that, around the border line 14 between the lip surface 12b and the side surface 12 c, a contact angle border line 14 a exists,which is provided or defined between the adjacent two regions thatdiffer from each other in contact angle with respect to the coatingliquid to such an extent as to demonstrate different identities incontact angle. If this is the case, it is preferred that a deviationbetween the contact angle border line 14 a and the border line 14 isless than or equal to 5 μm (see FIG. 4).

With reference next to FIGS. 7 to 9, comparative examples to the presentinvention are described.

As shown in FIG. 7, a coating die head 2, which includes agenerally-configured lip surface and a generally-configured sidesurface, is arranged with its terminal segment in close proximity to thesurface of a substrate 1 placed on a chuck 5. Next, the chuck 5 movesthe substrate 1 for displacement relative to the coating die head 2emitting liquefied resist, applying the emitted liquefied resist to forma coating layer 4 on the surface of the substrate 1. Subsequently,thickness uniformity of the layer 4 is accomplished by rotating thesubstrate 1 at a high speed. The reason why the thickness uniformitycannot be accomplished without rotating the substrate 1 is that theapplication process with the coating die head 2 cannot suppressthickness variation within the acceptable range due to stripes 4 a andsteps 4 b inevitably formed. This generally employed spin coatingimmediately after applying the resist to the substrate by the coatingdie head causes a cost increase because of two processes needed.

Next, description is made on what causes thickness variation in thecoating layer when the coating die head 2 carries out application ofcoating liquid to the substrate. As shown in FIG. 8, the coating diehead 2 has a slot 2 a for emitting resist (coating liquid) to beapplied, a lip 2 b having a lip surface 2 b extending outwardly from theslot 2 a in a direction generally normal to the slot 2 a, and a side 2 chaving a side surface 2 c extending outwardly from the lip surface ofthe lip 2 b and inclined thereto. During application of coating liquidto the surface of the substrate 1, the coating die head 2 forms coatingliquid lump (bead) 3 between the lip surface 2 b and the substrate 1. Ifthis bead 3 were stabilized to maintain its shape thereby to hold apoint A or B, at which the uppermost portion of the bead 3 of liquidfalls off the coating die head 2, always at an area where the lipsurface 2 b and side surface 2 c define therebetween a border line, thecoating layer 4 would be free from the undesired thickness variation.

However, the comparative example cannot maintain the point A or B alwaysat the area where the border line exists, allowing the liquid to flowaround from the lip surface 2 b to the side surface 2 c, causing motionof the liquid along the side surface 2 c as shown by arrows C as well asmotion of the liquid along the lip surface 2 b as shown by arrows D.Such motions of the liquid hamper stabilization of the bead 3, thuscausing the point A or B from moving to various locations deviated fromthe border line. If the point A or B moves at each of a plurality ofspaced points along the border line, stripes 4 a (see FIG. 7) extendingin a direction of movement of the substrate will appear, whereas if thepoint A or B moves to various locations continuously along the borderline, steps 4 b lying laterally with respect to the moving direction ofthe substrate 1 will appear.

In order to prevent the point A or B from moving to various locationsfor enhanced stabilization of bead 3, one may devise a coating die head2A, as shown in FIG. 9, which has an acute edge 2 d on or in parallel toa border line between a lip surface 2 b and the adjacent side surface 2c. This coating die head 2A, however, still fails to sufficientlyrestrain the point A or B from moving to various locations, although itprovides enhanced stabilization of the bead 3 more than the coating diehead 2 shown in FIG. 7 does. In FIG. 9, a reduction, in number, ofstripes and steps has been observed, but it is not appreciably largeenough to provide high precision coating required during fabrication ofcolor filters for crystal displays.

According to the present invention, the coating die head 12 cansufficiently enhance stabilization of the bead 3, thus preventing thestripes and steps from appearing in the coating layer 4.

EXAMPLE

Next, an embodiment according to the present invention is described.

-   -   (1) A coating die head: a coating die head 12    -   Material of a body of the coating die head 12: stainless steel    -   Lip surface 12 b: Width: 500 μm;        -   Surface: the same material as the body (stainless steel);        -   Surface roughness Rmax: 0.4 μm;        -   Contact angle with respect to coating liquid: about 7            degrees:    -   Side surface 12 c: Surface: Electroless plating of nickel;        -   Surface roughness Rmax: 0.4 μm;        -   Contact angle with respect to coating liquid: about 15            degrees:    -   Straightness of a border line between the lip surface 12 b and        the side surface 12 c: less than or equal to 5 μm/m:    -   (2) Coating Liquid    -   Color resist on solvent systems;    -   Viscosity: 5 cP    -   Surface tension: 25 dyne/cm:    -   (3) Coating Condition

As shown in FIG. 4, with the coating die head 12 oriented downward, asubstrate 1 was placed below the coating die head 12, and has been movedhorizontally at a speed of 80 mm/second to apply the coating liquid to adepth of about 10 μm.

-   -   (4) Result        -   Visual inspection on a coating layer after application of            the coating liquid to a substrate resulted in finding of no            stripes and steps. After drying this coating layer, the            coating layer measured 1.5 μm thick with thickness variation            less than or equal to ±2%. The thickness variation of the            coating layer fell in the acceptable range required for            fabrication of color filters. Use of spin coating during            fabrication of color filters was eliminated.

Because a contact angle of the side surface with respect to the coatingliquid is greater than a contact angle of the lip surface with respectto the coating liquid, the coating die head according to the presentinvention can hold a point, at which the uppermost portion of liquid ofbead falls off the coating die head, always at an area where the lipsurface and the side surface define therebetween a border line, therebyto provide sufficiently stabilized bead. This configuration is effectiveenough to prevent stripes and steps from appearing in the coating layerand also to suppress thickness variation satisfactorily. If it is usedduring a resist coating process of fabrication of color filters forliquid crystal displays, this implementation according to the presentinvention can carry out high precision coating required for thefabrication. Thus, this implementation according to the presentinvention can accomplish cost reduction by eliminating spin coating.

ANOTHER EMBODIMENT ACCORDING TO THE INVENTION

Referring to the drawings, another embodiment of the present inventionis hereinafter described in detail.

FIG. 10 is a perspective schematic view of another implementation of acoating die head 101 according to the present invention together with anenlarged view of a portion of this perspective view. FIG. 11 is aperspective schematic view given by enlarging a terminal segment of thiscoating die head 101.

This coating die head 101 has a slot 111 for emitting a coating liquidto be applied, a lip 112 located on a terminal segment 112, 113 of thecoating die head and having a lip surface 112 extending outwardly fromthe slot 111 in a direction generally normal to the slot 111, and a side113 located on the terminal segment 112, 113 and having a side surface113 extending outwardly from the lip surface of the lip 112 and inclinedthereto. The whole body of the coating die head 101 is made of stainlesssteel.

In this embodiment, the lip surface of the lip and the side surface ofthe side can be represented by reference numerals 112 and 113respectively.

The lip surface 112 extends in the normal direction over a width d,which width d normally ranges from 0.1 to 1.0 mm.

The lip surface 112 is a bare surface resulting from exposing the bodyof the coating die head 101 grounded to surface roughness 0.05 μm inRmax by ELID (ELectrolytic In-process Dressing) grinding. The surfaceroughness is herein expressed in terms of the maximum height, Rmax, overthe entire area of a surface scanned and measured in accordance withJapanese Industrial Standard JIS B 0601. The data on surface roughnesswere obtained by the contact stylus measurement method in accordancewith JIS B 0601.

Rmax 0.05 or 0.05 μm in Rmax means that the maximum height is 0.05 μm.JIS B 0601 corresponds to ISO 0486(1982), ISO 3276(1975), ISO4287-1(1984), ISO 4287-2(1984) and ISO 4288(1985).

The side surface 113 consists of a surface layer 114 formed by coatingor plating material having poor wettability with respect to the coatingliquid. Accordingly, the surface layer 114, serving as the side surface113, has poor wettability with respect to the coating liquid (a largecontact angle with respect to the coating liquid). In this embodiment,the surface layer 114 is formed by electroless plating of a mixturecontaining nickel (Ni) and 1 to 10 wt % of fluororesin.

If the coating liquid is in the form of liquefied resist generally usedfor the fabrication of color filters for liquid crystal displays, acontact angle of the lip surface 112 with respect to the coating liquidfalls in a range from 7 degrees to 10 degrees. If, under this condition,the surface layer 114 is formed by electroless plating of a mixturecontaining nickel (Ni) and 1 to 10 wt % of fluororesin, a contact angleof the side surface 113 with respect to the coating liquid amounts to 55degrees, and thus the difference in angle amounts to 40 degrees atleast. When the content of fluororesin is less than or equal to 10 wt %,the surface layer 114 is as hard as the bare body (Rockwell Hardness:HRC 45 to 55) and so has durability as much as the lip surface 112. Whenthe content of fluororesin is less than 1 wt %, the surface layer 114lose superiority to the lip surface of the lip 112 in contact angle withrespect to the coating liquid. When the content of fluororesin isgreater than 10 wt %, the surface layer 114 cannot maintain durabilityas much as the lip surface 112. It is necessary to form the surfacelayer 114 so that the surface layer 114 can extend to cover at least aregion, which might be covered by the spread of coating liquid duringcoating process.

As shown in FIG. 11, the surface layer 114 extends over the wholesurface area 113 and has an edge lying on a border line 115 between thelip surface 112 and the surface layer 114. The border line 115 providedbetween the lip surface 112 and the surface layer 114 on the sidesurface 113 is straight, and it has straightness and parallelness, withrespect to the slot 111, which are less than or equal to 2 μm/m.

In order to form the surface layer 114 to the edge exactly defining theborder line 115 having the straightness and parallelness less than orequal to 2 μm/m, material of the surface layer 114 is deposited, byplating or coating, over the entire surface area of not only the sidesurface 113, but also the lip surface 112 as shown in FIG. 12( a), andthen a portion of the material is removed, by polishing, for example, toexpose the lip surface 112 and the edge of the surface layer 114 asshown in FIG. 12( b). The data on straightness of the border line 115were obtained by the contact stylus measurement method in accordancewith JIS B 0601.

For application of the coating liquid using the coating die head 101,the terminal segment 112, 113 of the coating die head 101 is held inclose proximity to the surface of a substrate 102 placed on a chuck (notillustrated) as shown in FIG. 13, and the substrate 102 is movedrelative to the coating die head 101. The coating die head 101 emits thecoating liquid to be applied to the substrate 102, forming bead 103between the lip surface 112 and the substrate 102, applying a portionseparated from the bead 103 to the substrate 102.

FIG. 14( a) is a perspective view of the coating die head 101 emittingcoating liquid. As shown in FIG. 14( b), if a lip surface 112 of acoating die head 101 is grounded using free slurry in the conventionalmanner, the lip surface of the lip 112 is rough and involvesconsiderably great local changes in contact angle with respect to thecoating liquid, failing to allow smooth movement of the coating liquidin a bead growing direction laterally with respect to a direction ofdisplacement of a substrate relative to the coating die head, thusincreasing time required for build-up of bead 103 a. Accordingly, asshown in FIG. 15( a), the quantity of coating liquid consumed forinitial build-up of bead 103 a (this quantity being often called initialbead quantity) increases. Thus, thickness of the layer formed on thesubstrate 102 is increased remarkably within an area applied with thecoating liquid immediately after the start of application of the coatingliquid, providing an elongated fault range where the desired thicknessuniformity fails to be accomplished.

As shown in FIG. 14( c), if a lip 112 of a coating die head 101 isprocessed with ELID grinding process, the lip surface 112 has smoothsurface roughness. This surface roughness is smooth enough tosufficiently suppress local changes in contact angle with respect to thecoating liquid, allowing smooth movement of coating liquid in a beadgrowing direction laterally with respect to a direction of displacementof a substrate relative to the coating die head, thus shortening timerequired for build-up of bead 103 b. Accordingly, as shown in FIG. 5(b), the initial bead quantity for bead 103 b is reduced satisfactorily,thus shortening a fault range in a coating layer 104, where the desiredthickness uniformity fails to be accomplished, to a very small length(for example, less than or equal to 5 mm). If it is used during a resistcoating process of fabrication of color filters for liquid crystaldisplays, the coating die head 101 can carry out high precision coating(for example, the fault range less than or equal to 5 mm) required forthe fabrication.

The lip surface 112 processed with ELID grinding process to mirrorfinish has surface roughness less than or equal to 0.3 μm in Rmax, whichis smooth enough to sufficiently suppress local changes in contactangle. Therefore smooth movement of the coating liquid can be made in abead growing direction laterally with respect to a direction ofdisplacement of the substrate relative to the coating die head, thusshortening time required for build-up of bead 103. For furtherfacilitating smooth movement of the coating liquid to shorten the timerequired for the bead build-up, it is preferred that the surfaceroughness is less than or equal to 0.1 μm in Rmax. More preferably, thesurface roughness is less than or equal to 0.05 μm in Rmax.

As described before, the contact angle of the side surface 113 of thecoating die head 101 is greater than that of the lip surface 112. Theside surface 113 has poor wettability with respect to the coatingliquid. This configuration can maintain a point A or B, at which theuppermost portion of the bead 103 of liquid falls off the coating diehead 101, always at an area where the lip surface 112 with goodwettability and the side surface 113 with poor wettability definetherebetween the border line.

During application of the coating liquid to the substrate 102, the bead103 is kept stabilized, applying the coating liquid to the substrate 102without any stripes and steps conventionally experienced. Thus, it ispossible to form a coating layer 104 that has accomplished thicknessuniformity by suppressing thickness variation to a sufficiently lowlevel (for example, thickness variation within ±1.5% of the layerthickness). Accordingly, if it is used during a resist coating processof fabrication of color filters for liquid crystal displays, thiscoating die head 101 can carry out high precision coating (for example,thickness variation within ±1.5% of the layer thickness) required forthe fabrication.

In the above-described implementation, the lip surface 112 is formed ofthe bare surface of the body and the surface layer 114 of the sidesurface 113 has poor wettability (large contact angle), thus providingthe side surface 113 with a contact angle greater than that of the lipsurface. The present invention is not limited to this configuration,which is just one example of altering contact angles of the lip surfaceof the lip 112 and side surface of the side 113. Referring, for example,to FIG. 16, a coating die head 101A includes separate members ofdifferent materials as portions 116 and 117, respectively, which formthe lip surface 112 and side surface 113. Referring to FIG. 17, althougha coating die head 101B is made of the same material, the coating diehead 101B is formed by surface treatment to give a lip surface 112 moreroughness to provide good wettability (by reducing contact angle) and byanother surface treatment to give a side surface 113 less roughness toprovide poor wettability (by increasing contact angle). Using thesemeasures, the contact angle of the side surface 113 can be made greaterthan that of the lip surface 112. The contact angles of the lip surfaceand the side surface may be altered by appropriately combining aselection in material with a selection in surface treatment to provideroughness.

It is likely that, around the border line 115 between the side surface113 and the lip surface 112, a contact angle border line 115 a exits,which is provided or defined between the adjacent two regions thatdiffer from each other in contact angle with respect to the coatingliquid to such an extent as to demonstrate different identities incontact angle. If this is the case, it is preferred that a deviationbetween the contact angle border line 115 a and the border line 115 isless than or equal to 2 μm (see FIG. 13).

With reference next to FIGS. 18 to 20, comparative examples to thepresent invention are described.

As shown in FIG. 18, a coating die head 101, which includes agenerally-configured lip surface and a generally-configured sidesurface, is arranged with its terminal segment in close proximity to thesurface of a substrate 102 placed on a chuck 105. Next, the chuck 105moves the substrate 102 for displacement relative to the coating diehead 101 emitting liquefied resist, and applying the emitted liquefiedresist to form a coating layer 104. Subsequently, thickness uniformityof the layer 104 is accomplished by rotating the substrate 102. Byemploying spin coating immediately after applying the resist to thesubstrate by the coating die head, a cost is increased because of twoprocesses needed. Japanese Patent No. 3201195 discloses a coatingprocess in which thickness uniformity is accomplished by applyingcoating liquid to a substrate using a coating die head only. However,this known coating process is not satisfactory because it cannot meetthe specification demanded by current fabrication of color filters forliquid crystal displays. The specification states that a fault rangewhere the thickness uniformity fails to be accomplished, should be lessthan or equal to 5 mm in an applying direction as measured from a startpoint 104 a.

However, it is difficult to suppress the fault range within 5 mm in theapplying direction from the start point 104 a when using the coating diehead 101.

Next, it will be explained what causes a fault range where thicknessuniformity fails to be accomplished, within the adjacent area to thestart point 104 a when coating liquid is applied to the substrate by thecoating die head 101. As shown in FIG. 19, the coating die head 101 hasa slot 111 for emitting resist (coating liquid) to be applied, a lip 112having a lip surface extending outwardly from the slot 111 in adirection generally normal to the slot 111, and a side 113 having a sidesurface extending outwardly from the lip surface of the lip 112 andinclined thereto. During application of coating liquid to the surface ofthe substrate 102, the coating die head 101 forms coating liquid lump(bead) 103 between the lip surface 112 and the substrate 102. Ingeneral, the quicker bead builds up, the shorter is the fault rangewhere the thickness uniformity fails to be accomplished. However, infact, this fault range cannot be shortened because local changes incontact angle existing in the lip surface 112 fail to allow smoothmovement of coating liquid in a bead growing directions laterally withrespect to a direction of displacement of the substrate. The localchanges in contact angle remain in the lip surface 112 becausepolishing-dependent surface finish varies with different performancelevels of polishing machines and different skill levels of labor. As thecoating liquid is not allowed to flow smoothly and quickly, it takes along time for build-up of bead 103. Substantial quantity of coatingliquid is consumed for build-up of bead 103 (initial bead quantity).Thus, thickness is increased within the adjacent area to the startpoint, resulting in an increase in length of the fault range where thethickness uniformity fails to be accomplished.

Further, the thickness variation can not be suppressed by the coatingdie within an acceptable range, because stripes 141 and/or steps 142appear in the coating layer 104 as described below. Now, it will beexplained what causes thickness variation in the coating layer whencoating liquid is applied to the substrate by the coating die head 101.With reference to FIG. 19, if the bead 103 were stabilized to maintainits shape thereby to maintain a point A or B, at which the uppermostportion of the bead 103 of liquid falls off the coating die head 101,always at an area where the lip surface 112 and a side surface 113define therebetween a border line, the coating layer 104 would be freefrom the undesired thickness variation. However, in the comparativeexample, the point A or B can not be maintained at the area where theborder line exists, but instead the liquid flows around from the lipsurface 112 to the side surface 113, as a result the liquid moves alongthe side surface 113 as shown by arrow C as well as/along the lipsurface 112 as shown by arrows D. Such motions of the liquid hamperstabilization of the bead 103, thus failing to prevent the point A or Bfrom moving to various locations from the border line. If the point A orB moves to various locations at each of a plurality of spaced pointsalong the border line, stripes 141 (see FIG. 18) extending in adirection of movement of the substrate will appear, whereas if the pointA or B moves to various locations continuously along the border line,steps 142 lying laterally with respect to the moving direction of thesubstrate will appear.

In order to restrain the point A or B from moving to various locationsfor enhanced stabilization of bead 103, one may devise a coating diehead 101A, as shown in FIG. 20, which has an acute edge 118 on or inparallel to a border line between a lip surface 112 and the adjacentside. This coating die head 101A, however, fails to sufficientlyrestrain the point A or B from moving to various locations, although itprovides enhanced stabilization of the bead 103 more than the coatingdie head 101 shown in FIG. 19. Stripes and steps can be reduced, but itis not sufficient enough to provide high precision coating requiredduring fabrication of color filters for crystal displays.

According to the present invention, as the local changes in contactangle have been suppressed satisfactorily due to a reduction in surfaceroughness, the coating liquid is allowed to move smoothly and quickly,shortening time required for bead build-up. Accordingly, if it is usedduring a resist coating process of fabrication of color filters forliquid crystal displays, the coating die head incorporating thisconfiguration can carry out high precision coating required for thefabrication by shortening as best as possible a fault range wherethickness uniformity fails to be accomplished.

According to the present invention, a point at which the uppermostportion of bead of coating liquid falls off a coating die head can bemaintained always at an area where the lip surface and the side surfacedefine therebetween a border line. Accordingly, if the coating die headis used during a resist coating process of fabrication of color filtersfor liquid crystal displays, the coating die head incorporating theabove configuration can carry out high precision coating required forthe fabrication by suppressing as much as possible thickness variationin the coating layer.

If the coating die head is used during a resist coating process offabrication of color filters for liquid crystal displays, the coatingdie head according to the present invention can carry out high precisioncoating required for the fabrication by shortening as much as possible arange where thickness uniformity is not yet accomplished, as well as bysuppressing as much as possible thickness variation in the coatinglayer.

1. A coating die head with a slot for emitting coating liquid to beapplied to a substrate, comprising: a lip located on a terminal segmentof the coating die head and having a lip surface extending from theslot; and a side located on the terminal segment and having a sidesurface inclined to the lip surface; wherein the side surface and thelip surface are configured such that a contact angle of the side surfacewith respect to the coating liquid is greater than a contact angle ofthe lip surface with respect to the coating liquid; wherein a borderline is provided between the lip surface and the side surface and theborder line has straightness and parallelness, with respect to the slot,which are less than or equal to 5 μm/m; wherein, around the border line,a contact angle border line is provided between the adjacent surfaceregions that differ from each other in contact angle with respect to thecoating liquid; and wherein a deviation between the contact angle borderline and the border line is less than or equal to 5 μm.
 2. The coatingdie head as claimed in claim 1, wherein the side surface and the lipsurface are configured such that the contact angle of the side surfacewith respect to the coating liquid is greater than the contact angle ofthe lip surface with respect to the coating liquid by a difference, inangle, that is greater than or equal to 5 degrees.
 3. The coating diehead as claimed in claim 1, wherein surface material of the side surfaceis different from that of the lip surface.
 4. The coating die head asclaimed in claim 1, wherein surface roughness of the side surface isdifferent from that of the lip surface.
 5. A coating apparatuscomprising: a coating die head with a slot for emitting coating liquidto be applied to a substrate, the coating die head including a liplocated on a terminal segment of the coating die head and having a lipsurface extending from the slot; and a side located on the terminalsegment and having a side surface inclined to the lip surface, whereinthe side surface and the lip surface are configured such that a contactangle between the side surface and the coating liquid is greater than acontact angle between the lip surface and the coating liquid; and meansfor carrying out relative displacement between the substrate and thecoating die head with the terminal segment held in close proximity tothe substrate for application of the emitted coating liquid to thesubstrate; wherein a border line is provided between the lip surface andthe side surface and the border line has straightness and parallelness,with respect to the slot, which are less than or equal to 5 μm/m;wherein, around the border line, a contact angle border line is providedbetween the adjacent surface regions that differ from each other incontact angle with respect to the coating liquid; and wherein adeviation between the contact angle border line and the border line isless than or equal to 5 μm.
 6. A coating die head with a slot foremitting coating liquid to be applied to a substrate, comprising: a liplocated on a terminal segment of the coating die head and having a lipsurface extending from the slot; and a side located on the terminalsegment and having a side surface inclined thereto; wherein surfaceroughness of the lip surface expressed in terms of the maximum height,Rmax, measured in accordance with Japanese Industrial Standard JIS B0601 is less than or equal to 0.3 μm; wherein the side surface and thelip surface are configured such that a contact angle of the side surfacewith respect to the coating liquid is greater than a contact angle ofthe lip surface with respect to the coating liquid; wherein, around aborder line between the lip surface and the side surface, a contactangle border line is provided between the adjacent regions that differfrom each other in contact angle with respect to the coating liquid; andwherein a deviation between the contact angle border line and the borderline is less than or equal to 2 μm.
 7. The coating die head as claimedin claim 6, wherein the lip surface is of mirror finish resulting fromsuper fine grinding.
 8. The coating die head as claimed in claim 6,wherein the lip surface is of mirror finish resulting from electrolyticin-process dressing (ELID) grinding.
 9. The coating die head as claimedin claim 6, wherein the side surface is made of electroless plating of amixture containing nickel (Ni) and 1 to 10 wt % of fluororesin.
 10. Thecoating die head as claimed in claim 6 wherein surface roughness of theside surface is different from that of the lip surface.
 11. The coatingdie head as claimed in claim 6, wherein a border line is providedbetween the lip surface and the side surface, and the border line hasstraightness and parallelness, with respect to the slot, which are lessthan or equal to 2 μm/m.